6D. 11

[Kaitlin Joya 1I]

Decide whether an aqueous solution of each of the following slats has a pH equal to, greater than, or less than 7. If not neutral, write a chemical equation to justify your answer.
e) AlCl3

The answer for this is pH < 7, and the equation given in the solution manual is Al(H2O)6^(3+) + H2O -> Al(H2O)5OH^(2+)

I am not sure if the solution manual does not correlate to the same question or something, but how do you get that equation from AlCl3? How do you know there are 6 molecules of H2O for Al and then another H2O?

[Carlotta Gherardi 2J]

Hi,

small, highly charged metal cations like Al, do not have protons to donate on their own. They can act as acids because in solution, the electrons from the oxygen in water are pulled towards Al, weakening the O-H bond, making protons now available to be donated. Therefore, whenever you consider small, highly charged metal cations as acids you have to consider them in solution: they are always surrounded by 6 molecules of H2O.

Hope this helps!

[Ethan Mai 1D]

Would Cl affect the pH of the solution, since it is also a component of the salt which dissociates? Why wouldn't the solution be neutral instead, since it is possible for Cl to act as a proton acceptor?

[Melody_Tapia_1J]

Would Cl affect the pH of the solution, since it is also a component of the salt which dissociates? Why wouldn't the solution be neutral instead, since it is possible for Cl to act as a proton acceptor?

Cl has no overall effect on the pH of the solution. Cl is an anion, which means that it's the conjugate base of an acid. More specifically, Cl is a conjugate base of a strong acid. Meaning that Cl is a weak base and therefore a "neutral anion" that doesn't have an effect on the pH.